Described below is a method for operating a motor vehicle having a first detection device, which uses radio waves, for a wireless key and a second detection device, which has a smaller detection range than the first detection device, for the key, wherein operation of an operator control element for switching the motor vehicle on and/or off is followed by performance of a search process using the first detection device and then, if a key associated with the motor vehicle has not been found by the first detection device, performance of a search process using the second detection device from a fallback instant. In addition, a description is provided of a motor vehicle in which the method is used.
Vehicle systems have already been proposed in the related art that allow the motor vehicle to be unlocked without using a key and/or allow the motor vehicle to be started without using a key. In this case, a wireless key associated with the motor vehicle is used, which the driver or the person locking and/or unlocking the motor vehicle, possibly even a passenger, carries with him such that the key can be detected by the motor vehicle. The underlying detection in this case is effected wirelessly using radio signals, such a key possibly including a chip, for example, an HFID chip.
If the presence of the key associated with the motor vehicle is supposed to be detected, for example because an operator control element for starting the motor vehicle has been operated, a first detection device becomes active, for example when actuated by a controller of the motor vehicle. The first detection device uses radio signals that cover the entire motor vehicle, possibly even an area outside the motor vehicle. In addition, for some applications it is desirable to obtain a location statement for the position of the wireless key as well.
A first detection device can include a plurality of transmission devices installed in the motor vehicle that transmit a request signal on a first frequency or in a first frequency band, which request signal is received by the key and may also contain the power for operating the key. Otherwise, the wireless key may also contain a battery or some other energy store. Following transmission of the request signal, a reception mode is activated in which a plurality of reception devices distributed over the motor vehicle, which may correspond to the transmission devices (transmission/reception devices), await an identification signal from the key as a response signal.
When the key or the transponder that is present in the key receives the request signal, provision may be made for the request signal to be decoded and output again with new coding in a different frequency band. By way of example, the request signal can be transmitted on an LF frequency in the region of 20 kHz, whereas the response signal used as an identification signal may be in the HF band or in the UHF band. The reception devices receive the response signal used as an identification signal and forward it to the controller, which checks whether the received, coded identification signal, which therefore contains a piece of identification information as a result of the coding, is coded correctly, and has therefore been transmitted by the key associated with the motor vehicle. If the check is positive, a key associated with the motor vehicle has been detected wirelessly (and therefore a key has been detected and authenticated), and the motor vehicle can be unlocked and started, for example.
In this case, the use of a plurality of reception devices has the advantage that it is also possible to establish the band that contains the key, for example using propagation time differences and/or by evaluating signal strengths and the like. By way of example, it is thus possible to establish whether the key is inside the motor vehicle or outside the motor vehicle.
If, when an operator control element for switching the motor vehicle on and/or off is operated, the search process using the first detection device does not detect a key associated with the motor vehicle, this can have various causes. By way of example, a short-term interference source is possible in radio communication (HF or LF). It is also conceivable for the key not yet to be in the motor vehicle, for example if the passenger who is carrying the key has not yet got in. A third possibility is that the energy store associated with the transponder of the key, for example a battery, is flat. Finally, a system error is also conceivable. So as nevertheless to allow the motor vehicle to be activated, the use of a second detection device that is based on a different wireless principle has been proposed as a fall-back solution. Therefore, if the key associated with the motor vehicle is not found using the first detection device, an instruction to use the second detection device is output to the user and the second detection device is activated. In this case, the second detection device is usually based on a much smaller detection range than the first detection device. By way of example, the second detection device may include a transponder coil that excites a second transponder of the key, and/or may be in the form of an NFC (near field communication) device, and could therefore have a range of 10 cm or less. The second detection device then has an associated area in the interior of the motor vehicle, with the driver being informed by the instruction that the wireless key now needs to be taken to this area in the detection range of the second detection device. By way of example, it is conceivable for a transponder coil of the second detection device to be arranged behind a cover. Attempts are therefore now made to find and authenticate the key associated with the motor vehicle using the second detection device. Therefore, a permanent switch is made to a search process using the second detection device. The key may be provided with a second transponder that is associated with the second detection device, or the first transponder of the key, which transponder is associated with the first detection device, may also be associated with the second detection device. When the key associated with the motor vehicle is found using the second detection device, the motor vehicle is switched on.
A disadvantage in this case is that the user imperatively must bring the wireless key into the detection range of the second detection device in order to detect the motor vehicle, even if there is only short-term interference or the operator control element has simply been operated too early.